it will probably have to extend from the rim slightly must be plastic due to how much it would cost if aluminum not sure if the power generated would be enough
I’m sure it could be done by some one who was clever enough. The problem is that it would take energy to generate the lift, this energy would most likely come from the yoyos spin, reducing the spin time. It would probably also make the yoyo quite unstable.
No, because the yoyo is round and spinning any force it generated would be equal in all directions. So any lift generated would be canceled by an equal amount of downward force also generated.
They would have to be very long, it would most likely not work due to the fact that the wind generated would go down onto the yoyo and not the ground and generate force.
While an unaltered yoyo would have the force in each direction if you were to have something hanging from the axle, like half a z-stack etc., to disrupt the downwards force then the force generated could (theoretically) always be opposite to that of gravity if the plane of the yoyo is normal to the ground.